The subject matter of the present invention pertains to a raster scan frame digitizer capable of digitizing an image displayed on a cathode ray tube (CRT) and storing the digital values representative of said image in a memory.
When an image is displayed on a cathode-ray tube (CRT), for example, it may be necessary to produce photocopies of the displayed image. Furthermore, it may be necessary to enhance the image, or format the image somewhat differently on the photocopy than that which is displayed on the CRT. Consequently, one method of accomplishing this objective, is to digitize the image, and to store the digital values representative of the image in a memory, so that either the image or the enhanced, reformatted version thereof may be re-created on hardcopies from the digital values.
During the digitization of the image, the image presented on the CRT must remain stationary. However, if the image is continually moving or otherwise changing, it is desirable to decrease the time required to digitize the stationary image displayed on the CRT and thereby decrease the time required for the CRT image to remain stationary. The stationary image may be digitized to accomplish several objectives. It may be necessary to process the image, digitally, in real time. It may also be necessary to produce hard copies of the stationary image, or it may be necessary merely to store the image in a memory for the purpose of formatting the image differently.
In order to process the image, digitally, in real time, it is necessary to digitize the image more rapidly than would be necessary if hard copies of the image were being made or if the image was being stored in the memory In order to digitize the image more rapidly, a more costly system digitizer is needed. However, with this more costly system digitizer, an improvement in image resolution inherently results in a limitation in the system bandwidth. If one needed merely to produce hard copies of the image, or to store the digitized image in the memory, it is not necessary to digitize the image more rapidly. As a result, it is not necessary to use such a costly system digitizer. Therefore, a further system digitizer is needed which will digitize the stationary image less rapidly, relative to the aforementioned more costly system digitizer, and, as a result, will be less costly, will produce a hard copy reproduction of the image having a better resolution and will have associated therewith a better bandwidth relative to the aforementioned more costly system digitizer of the prior art.